U.S. patent number 10,272,619 [Application Number 14/281,305] was granted by the patent office on 2019-04-30 for manufacture of a resin infused one-piece composite truss structure.
This patent grant is currently assigned to The Boeing Company. The grantee listed for this patent is The Boeing Company. Invention is credited to Andrew K. Glynn, Peter J. Lockett, David A. Pook, Manning J. Scarfe.
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United States Patent |
10,272,619 |
Lockett , et al. |
April 30, 2019 |
Manufacture of a resin infused one-piece composite truss
structure
Abstract
A composite truss structure may have a first facesheet, a second
facesheet, and a plurality of truss elements joined with the first
facesheet and the second facesheet at nodes to form a one-piece
structure. The composite truss structure may be formed by a method
comprising preparing a dry fabric mold by: 1) placing a first dry
fabric layer on a tool, 2) placing a first layer of fabric-loaded
mandrels on the first dry fabric layer, 3) placing a second layer
of the fabric-loaded mandrels on the first layer of fabric-loaded
mandrels, and 4) placing a second dry fabric layer over the
fabric-loaded mandrels. The method may further comprise infusing
the dry fabric mold with a resin, and curing the resin to provide
the nonflexible composite truss structure.
Inventors: |
Lockett; Peter J. (Thornbury,
AU), Scarfe; Manning J. (Ascot Vale, AU),
Glynn; Andrew K. (Kensington, AU), Pook; David A.
(Malvern East, AU) |
Applicant: |
Name |
City |
State |
Country |
Type |
The Boeing Company |
Chicago |
IL |
US |
|
|
Assignee: |
The Boeing Company (Chicago,
IL)
|
Family
ID: |
53174795 |
Appl.
No.: |
14/281,305 |
Filed: |
May 19, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150328845 A1 |
Nov 19, 2015 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C
70/44 (20130101); B29C 70/543 (20130101); B30B
15/062 (20130101); B29C 70/446 (20130101); B29D
24/002 (20130101); B29D 24/00 (20130101); B29D
24/004 (20130101); B29C 70/443 (20130101); B64C
1/06 (20130101); B29C 70/545 (20130101); Y02T
50/43 (20130101); Y02T 50/40 (20130101); B29K
2105/0827 (20130101); Y10T 428/24149 (20150115) |
Current International
Class: |
B29C
70/44 (20060101); B29C 70/54 (20060101); B29D
24/00 (20060101); B30B 15/06 (20060101); B64C
1/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
1454277 |
|
Nov 2003 |
|
CN |
|
103687788 |
|
Mar 2014 |
|
CN |
|
0967147 |
|
Dec 1999 |
|
EP |
|
0967147 |
|
Sep 2003 |
|
EP |
|
2396168 |
|
Aug 2010 |
|
RU |
|
1991014565 |
|
Oct 1991 |
|
WO |
|
Other References
European Search Report for Related Application No. EP15165217.9;
Report dated Sep. 15, 2015. cited by applicant .
Chinese Office Action for Related Application No. 201510088050.4;
Report dated Jun. 6, 2018. cited by applicant .
GCC Examination Report for Related Application No. GC 2015-29406;
Report dated Feb. 18, 2018. cited by applicant .
Russian Office Action for related application No. 2015/102214;
dated Aug. 16, 2018. cited by applicant .
Australian Search Report for Related Application No. AU2015200451;
Report dated Feb. 11, 2019. cited by applicant .
European Search Report for Related Application No. EP18180371.9;
Report dated Nov. 13, 2018. cited by applicant.
|
Primary Examiner: Daniels; Matthew J
Attorney, Agent or Firm: Miller, Matthias & Hull LLP
Claims
What is claimed is:
1. A method for fabricating a composite truss structure having a
core with a plurality of truss elements, comprising: preparing a
dry fabric mold by a method comprising placing a first dry fabric
layer on a tool having a non-corrugated surface, and placing a
first layer of fabric-loaded mandrels on the first dry fabric layer
to create a corrugated surface, each of the fabric-loaded mandrels
having a major axis and including a dry fabric tube wrapped around
a mandrel, the first layer of fabric-loaded mandrels including a
row of the fabric-loaded mandrels aligned in abutment and in
parallel along the major axes of the fabric-loaded mandrels, each
of the fabric-loaded mandrels of the row having a same
cross-sectional shape that becomes progressively smaller across the
row to provide a wedge structure; infusing the dry fabric mold with
a resin; curing the resin to provide the composite truss structure;
and repeatedly slicing the composite truss structure along an axis
perpendicular to the major axes to provide a plurality of
individual components each having the composite truss
structure.
2. The method of claim 1, wherein preparing the dry fabric mold
further comprises placing a second layer of fabric-loaded mandrels
on the first layer of fabric-loaded mandrels by positioning each of
the fabric-loaded mandrels of the second layer in a respective one
of grooves formed on the corrugated surface, the second layer of
fabric-loaded mandrels including a second row of the fabric-loaded
mandrels aligned in abutment and in parallel along the major axes
of the fabric-loaded mandrels, each of the fabric-loaded mandrels
of the second row having a same cross-sectional shape that becomes
progressively smaller across the second row to provide the wedge
structure.
3. The method of claim 2, wherein preparing the dry fabric mold
further comprises placing a second dry fabric layer over the second
layer of fabric-loaded mandrels.
4. The method of claim 3, further comprising preparing each of the
fabric-loaded mandrels by pulling the dry fabric tube over the
mandrel or by braiding the dry fabric tube over the mandrel.
5. The method of claim 3, further comprising removing the mandrels
from the composite truss structure after curing the resin to
provide the composite truss structure.
6. The method of claim 5, wherein removing the mandrels from the
composite truss structure comprises treating the mandrels with a
solvent.
7. The method of claim 5, wherein preparing the dry fabric mold
further comprises inserting a filler material in each gap in the
dry fabric mold.
8. The method of claim 5, wherein each of the fabric-loaded
mandrels has a top and a base, and wherein placing the first layer
of fabric-loaded mandrels on the first dry fabric layer comprises
placing the base of each of the fabric-loaded mandrels in contact
with the first dry fabric layer.
9. The method of claim 8, wherein placing the second layer of
fabric-loaded mandrels on the first layer of fabric-loaded mandrels
comprises placing the top of each of the fabric-loaded mandrels of
the second layer in contact with a bottom of a respective one of
the grooves formed on the corrugated surface.
10. The method of claim 1, wherein preparing the dry fabric mold
further comprises: placing additional layers of fabric-loaded
mandrels over the first layer of fabric-loaded mandrels; and
placing a plurality of dry fabric layers at desired locations
between the layers of fabric-loaded mandrels.
11. The method of claim 1, wherein repeatedly slicing the composite
truss structure along an axis parallel to the major axes to provide
a plurality of individual components each having the composite
truss structure comprises repeatedly slicing the entire composite
truss structure into the plurality of individual components.
12. A method for fabricating a number of individual components each
having a nonflexible composite truss structure formed from a
fiber-reinforced resin material and having a first facesheet, a
second facesheet, and a reinforcing core of truss elements fused
with the first facesheet and the second facesheet, the method
comprising: preparing a dry fabric mold by a method comprising
placing a first dry fabric layer on a tool, placing a first layer
of fabric-loaded mandrels on the first dry fabric layer to create a
corrugated surface having a plurality of grooves, placing a second
layer of fabric-loaded mandrels on the first layer of fabric-loaded
mandrels by positioning each of the fabric-loaded mandrels of the
second layer in a respective one of the grooves of the corrugated
surface, each of the fabric-loaded mandrels of the first layer and
the second layer having a major axis and including a dry fabric
tube wrapped around a mandrel, each of the first layer and the
second layer including a row of the fabric-loaded mandrels aligned
in abutment and in parallel along the major axes of the
fabric-loaded mandrels, each of the fabric-loaded mandrels of the
row having a same cross-sectional shape that becomes progressively
smaller across the row to provide a wedge structure, and placing a
second dry fabric layer over the fabric-loaded mandrels; infusing
the dry fabric mold with a resin; curing the resin to provide a
larger panel having the composite truss structure, the larger panel
being sized to provide the number of individual components; and
repeatedly slicing the larger panel along an axis perpendicular to
the major axes to provide the number of individual components each
having the nonflexible composite truss structure.
13. The method of claim 12, wherein each of the fabric-loaded
mandrels include a top and a base that is wider than the top, and
wherein placing the first layer of fabric-loaded mandrels on the
first dry fabric layer further comprises aligning the fabric-loaded
mandrels in parallel on the first dry fabric layer with the base of
each fabric-loaded mandrel contacting the first dry fabric
layer.
14. The method of claim 13, wherein placing the second layer of
fabric-loaded mandrels on the first layer of fabric-loaded mandrels
further comprises inserting the top of each of the fabric-loaded
mandrels of the second layer into a respective one of the grooves
of the corrugated surface.
15. The method of claim 14, further comprising preparing each of
the fabric-loaded mandrels by pulling the dry fabric tube over the
mandrel.
16. The method of claim 14, further comprising preparing each of
the fabric-loaded mandrels by braiding the dry fabric tube over the
mandrel.
17. The method of claim 14, further comprising removing the
mandrels from the composite truss structure after curing the
resin.
18. The method of claim 17, wherein removing the mandrels from the
composite truss structure comprises treating the mandrels with a
solvent.
19. The method of claim 17, wherein the mandrels are water-soluble,
and wherein removing the mandrels from the composite truss
structure comprises treating the mandrels with water.
20. A method for fabricating a composite truss structure having a
first facesheet, a second facesheet, and a reinforcing core of
truss elements fused with the first facesheet and the second
facesheet, the method comprising: preparing a dry fabric mold by a
method comprising placing a first dry fabric layer on a flat tool,
aligning a first layer of fabric-loaded mandrels on the first dry
fabric layer to provide a corrugated surface having a plurality of
parallel grooves, each of the fabric-loaded mandrels having a major
axis and including a dry fabric tube wrapped around a mandrel
having a top and a base that is wider than the top, the first layer
of fabric-loaded mandrels including a row of the fabric-loaded
mandrels aligned in abutment and in parallel along the major axes
of the fabric-loaded mandrels, each of the fabric-loaded mandrels
of the row having a same cross-sectional shape that becomes
progressively smaller across the row, placing a second layer of
fabric-loaded mandrels on the first layer of fabric-loaded mandrels
by inserting the top of each of the fabric-loaded mandrels of the
second layer in a respective one of the parallel grooves, the
second layer of fabric-loaded mandrels including a second row of
the fabric-loaded mandrels aligned in abutment and in parallel
along the major axes of the fabric-loaded mandrels, each of the
fabric-loaded mandrels of the second row having a same
cross-sectional shape that becomes progressively smaller across the
second row, and placing a second dry fabric layer over the
fabric-loaded mandrels to provide the dry fabric mold, the first
and second dry fabric layers being planar and tapering toward each
other to a point to provide a wedge structure, the dry fabric mold
providing a fabric skeleton for the composite truss structure;
infusing the dry fabric mold with a resin; curing the resin to
provide the composite truss structure; removing the mandrels to
provide cavities in the composite truss structure, the cavities
having the same cross-sectional shape as the mandrels; and
repeatedly slicing the composite truss structure through the
cavities to provide a plurality of individual components having the
composite truss structure.
21. The method of claim 20, wherein the mandrels are removed
manually or by tool-assisted removal.
Description
FIELD
The present disclosure generally relates to resin-infused and
nonflexible composite truss structures, and more specifically,
relates to methods for manufacturing one-piece composite truss
structures having two facesheets and a core of truss elements.
BACKGROUND
Fiber-reinforced resin materials are lightweight and high-strength
materials that are gaining increasing use for component fabrication
in various applications, including aerospace technologies.
Fiber-reinforced resin materials are a composite of woven or
nonwoven fiber fabric and a resin matrix. In some cases,
fiber-reinforced resin materials may be fabricated as structures
having intrinsic stiffening capabilities to further extend the
strength and durability of any components formed from these
materials. Composite sandwich constructions, for example, may
consist of a rigid core between two composite facesheets of
fiber-reinforced resin. As one example, U.S. Pat. No. 6,508,910
describes composite sandwich constructions formed from a rigid
honeycomb core between two facesheets of fiber fabric
pre-impregnated with resin (or "prepreg" fabric). While effective,
prepreg architectures such as these may require a complex series of
manufacturing steps involving multiple curing cycles and debulking
steps. In addition, the cutting of honeycomb-stiffened composite
sandwich structures into a number of components may be difficult,
as any exposed, cut edges of honeycomb units may reduce product
durability or may require additional processing.
Truss structures consist of one or more triangular or trapezoidal
truss elements connected at "nodes". While truss structures are
widely appreciated for their ability to provide a rigid framework
in construction applications, it remains a challenge to integrate
truss elements as stiffening structures in composite sandwich
architectures using efficient manufacturing processes. Although a
method for manufacturing flexible composite truss structures with a
single facesheet has been described in U.S. Pat. No. 8,651,419, the
resulting truss structures disclosed therein requires attachment to
a rigid support surface such as an airframe to provide a stiffened
structure.
Clearly, there is a need for efficient manufacturing methods that
provide access to nonflexible, stiffened composite truss structures
for various applications.
SUMMARY
In accordance with one aspect of the present disclosure, a method
for fabricating a composite truss structure having a core with a
plurality of truss elements is disclosed. The method may comprise
preparing a dry fabric mold by placing a first dry fabric layer on
a tool having a non-corrugated surface, and placing a first layer
of fabric-loaded mandrels on the first dry fabric layer to create a
corrugated surface, wherein each of the fabric-loaded mandrels
includes a dry fabric tube wrapped around a mandrel. The method may
further comprise infusing the dry fabric mold with a resin, and
curing the resin to provide the composite truss structure.
In another refinement, preparing the dry fabric mold may further
comprise placing a second layer of fabric-loaded mandrels on the
first layer of fabric-loaded mandrels by positioning each of the
fabric-loaded mandrels of the second layer in a respective one of
grooves formed on the corrugated surface.
In another refinement, preparing the dry fabric mold may further
comprise placing a second dry fabric layer over the second layer of
fabric-loaded mandrels.
In another refinement, preparing the dry fabric mold may further
comprise placing one or more additional layers of fabric-loaded
mandrels over the second layer of fabric-loaded mandrels, and
placing a second dry fabric layer over one or more of the first,
second, or additional layers of fabric-loaded mandrels.
In another refinement, the method may further comprise preparing
each of the fabric-loaded mandrels by pulling the dry fabric tube
over the mandrel or by braiding the dry fabric tube over the
mandrel.
In another refinement, the method may further comprise removing the
mandrels from the composite truss structure.
In another refinement, removing the mandrels from the composite
truss structure may comprise treating the mandrels with a
solvent.
In another refinement, the method may further comprise slicing the
composite truss structure into a plurality of individual
components.
In another refinement, infusing the dry fabric mold with the resin
may comprise: 1) placing a vacuum bag over the dry fabric mold, 2)
evacuating the vacuum bag, and 3) drawing the resin into the vacuum
bag to infuse the dry fabric mold with the resin.
In another refinement, preparing the dry fabric mold may further
comprise inserting a filler material in each gap in the dry fabric
mold.
In another refinement, each of the fabric-loaded mandrels may have
a top and base, and placing the first layer of fabric-loaded
mandrels on the first dry fabric layer may comprise placing the
base of each of the fabric-loaded mandrels in contact with the
first dry fabric layer.
In another refinement, placing the second layer of fabric-loaded
mandrels on the first layer of fabric-loaded mandrels may comprise
placing the top of each of the fabric-loaded mandrels of the second
layer in contact with a bottom of a corresponding one of the
grooves formed on the corrugated surface.
In accordance with another aspect of the present disclosure, a
composite truss structure is disclosed. The composite truss
structure may comprise a first facesheet, a second facesheet, and a
reinforcing core between the first facesheet and the second
facesheet. The reinforcing core may include a plurality of truss
elements each joined with the first facesheet and the second
facesheet at nodes to form a one-piece structure. The composite
truss structure may be formed by infusion of a dry fabric mold with
a resin followed by curing of the resin.
In another refinement, the cured resin may fuse the first
facesheet, the second facesheet, and the plurality of truss
elements together as the one-piece structure.
In another refinement, the first facesheet and the second facesheet
may extend parallel to each other.
In another refinement, the first facesheet and the second facesheet
may be angled with respect to each other.
In another refinement, each of the truss elements may be triangular
in cross-section.
In another refinement, each of the truss elements may be
trapezoidal in cross-section.
In another refinement, each of the truss elements may be
rectangular in cross-section.
In accordance with another aspect of the present disclosure, a
composite truss structure having a first facesheet, a second
facesheet, and a reinforcing core including a plurality of truss
elements joined with the first facesheet and the second facesheet
to form a unitary structure is disclosed. The composite truss
structure may be fabricated by a method comprising preparing a dry
fabric mold by: 1) placing a first dry fabric layer on a tool, 2)
placing a first layer of fabric-loaded mandrels on the first dry
fabric layer to create a corrugated surface, 3) placing a second
layer of fabric-loaded mandrels on the first layer of fabric-loaded
mandrels by positioning each of the fabric-loaded mandrels of the
second layer in a respective one of grooves formed in the
corrugated surface, wherein each of the fabric-loaded mandrels of
the first layer and the second layer include a dry fabric tube
wrapped around a mandrel, and 4) placing a second dry fabric layer
over the fabric-loaded mandrels. The method may further comprise
infusing the dry fabric mold with a resin, and curing the resin to
provide the composite truss structure.
The features, functions, and advantages that have been discussed
can be achieved independently in various embodiments or may be
combined in yet other embodiments further details of which can be
seen with reference to the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is front view of a composite truss structure, constructed in
accordance with the present disclosure.
FIG. 2 is a perspective view of the composite truss structure of
FIG. 1.
FIG. 3 is a perspective view of an aerodynamic wedge structure
having the composite truss structure, constructed in accordance
with the present disclosure.
FIG. 4 is a perspective view, schematically illustrating the
preparation of a fabric-loaded mandrel, in accordance with a method
of the present disclosure.
FIG. 5 is a front view, schematically illustrating the placement of
a first dry fabric layer on a tool, in accordance with a method of
the present disclosure.
FIG. 6 is a front view, schematically illustrating the placement of
a first layer of fabric-loaded mandrels on the first dry fabric
layer, in accordance with a method of the present disclosure.
FIG. 7 is a perspective view of a corrugated surface provided by
the first layer of fabric-loaded mandrels, constructed in
accordance with the present disclosure.
FIG. 8 is a front view, schematically illustrating the placement of
a second layer of fabric-loaded mandrels on the first layer of
fabric-loaded mandrels, in accordance with a method of the present
disclosure.
FIG. 9 is a front view of multiple layers of fabric-loaded mandrels
stacked on the first dry fabric layer, constructed in accordance
with the present disclosure.
FIG. 10 is a front view, schematically illustrating the placement
of a second dry fabric layer over the fabric-loaded mandrels, in
accordance with a method of the present disclosure.
FIG. 11 is a front view of a dry fabric mold, constructed in
accordance with the present disclosure.
FIG. 12 is a front view of a dry fabric mold similar to FIG. 11,
but having a second dry fabric layer placed over multiple layers of
fabric-loaded mandrels, constructed in accordance with the present
disclosure.
FIG. 13 is a front view similar to FIG. 12, but having second dry
fabric layers placed between the layers of fabric-loaded mandrels,
constructed in accordance with the present disclosure.
FIG. 14 is a front view of detail 14 of FIG. 11, schematically
illustrating the filling of gaps in the dry fabric mold with a
filler material, in accordance with a method of the present
disclosure.
FIG. 15 is a front view, schematically illustrating resin infusion
and curing of the dry fabric mold to provide the composite truss
structure, in accordance with a method of the present
disclosure.
FIG. 16 is a perspective view, schematically illustrating the
removal of the mandrels from the composite truss structure, in
accordance with a method of the present disclosure.
FIG. 17 is a perspective view, schematically illustrating the
removal of the mandrels from the composite truss structure by
treatment with a solvent, in accordance with a method of the
present disclosure.
FIG. 18 is a perspective view, schematically illustrating slicing
of the composite truss structure into individual components, in
accordance with a method of the present disclosure.
FIG. 19 is a flowchart illustrating a sample sequence of steps
which may be involved in the manufacture of components having the
composite truss structure, in accordance with a method of the
present disclosure.
It should be understood that the drawings are not necessarily drawn
to scale and that the disclosed embodiments are sometimes
illustrated schematically. It is to be further appreciated that the
following detailed description is merely exemplary in nature and is
not intended to limit the invention or the application and uses
thereof. Hence, although the present disclosure is, for convenience
of explanation, depicted and described as certain illustrative
embodiments, it will be appreciated that it can be implemented in
various other types of embodiments and in various other systems and
environments.
DETAILED DESCRIPTION
Referring now to the drawings, and with specific reference to FIGS.
1 and 2, a nonflexible composite structure 10 is shown. The
nonflexible composite structure 10 may have a composite sandwich
construction with a first facesheet 12, a second facesheet 14, and
a reinforcing core 16 between the first facesheet 12 and the second
facesheet 14. The reinforcing core 16 may consist of one or more
truss elements 18 that may be fused with the first facesheet 12 and
the second facesheet 14 at nodes 20 to provide a one-piece or
unitary structure. The truss elements 18 may be aligned and
continuous along the length (l) of the composite structure 10, as
shown in FIG. 2. The nonflexible composite structure 10 may be
stiff by virtue of its two facesheets 12, 14, its reinforcing core
16, as well as its material construction. Given its rigid
construction, it may be capable of providing the structural
framework for a variety of components without assistance from
additional reinforcing elements or support structures. As a
non-limiting example, the composite truss structure 10 may provide
a rigid framework for various airframe components, although it may
be used in other applications as well. Moreover, the composite
truss structure 10 may be manufactured more efficiently than
comparable composite sandwich structures of the prior art (see
additional details below).
The facesheets 12 and 14 may have a smooth and flattened structure,
or they may be curved or bent in some regions depending on the
application. In addition, the facesheets 12 and 14 may extend
parallel to one another, as shown in FIGS. 1 and 2, or they may be
angled with respect to one another, as shown by an aerodynamic
wedge structure 22 in FIG. 3. Although the truss elements 18 are
shown as being triangular in cross-section in FIGS. 1-3, they may
have various other shapes as well such as, but not limited to,
trapezoidal or rectangular shapes. Furthermore, the truss elements
18 may have sharp edges (see FIGS. 1-3) or rounded edges, and the
relative sizes, shapes, and spacings between the truss elements 18
may vary as well.
The composite truss structure 10 may be formed from a
fiber-reinforced resin material that may consist of a fabric of
woven or nonwoven fibers embedded in a cured resin matrix. The
fibers in the fabric may be carbon fibers, glass fibers, aramid
fibers, or any other suitable fiber or combinations of fibers. In
addition, the cured resin may fuse the facesheets 12 and 14 and the
truss elements 18 together to provide the composite truss structure
10 with its one-piece construction (see further details below).
FIGS. 4-18 schematically illustrate a series of steps and
intermediate structures that may be involved in the fabrication of
components having the nonflexible composite truss structure 10.
Starting with FIG. 4, a mandrel 24 having a cross-sectional shape
corresponding with the desired truss elements 18 may be wrapped
with a dry fabric tube 26 to provide a fabric-loaded mandrel 28, as
shown. Wrapping of the mandrel 24 with the dry fabric tube 26 may
be achieved by pulling the dry fabric tube 26 over the mandrel 24
tightly to provide a tight-fitting fabric covering that is
wrinkle-free or at least substantially wrinkle-free, such that the
fabric-loaded mandrel 28 may conform to the shape of the mandrel
24. Alternatively, wrapping of the mandrel 24 with the dry fabric
tube 26 may be achieved by braiding a dry fabric tube 26 over the
mandrel 24. The dry fabric tube 26 may consist of a fabric of
braided or woven fibers that is "dry" (i.e., not pre-impregnated
with a resin). If the desired truss elements are triangular in
cross-section, the mandrel 24 may have a triangular prism shape, as
shown, or it may have other shapes if different types of truss
elements are desired. In general, however, the mandrel
24/fabric-loaded mandrel 28 may have a base 30 with a greater width
(w) than a top 32, unless of course the mandrel 24 is rectangular
in cross-section. Furthermore, the mandrel 24/fabric-loaded mandrel
28 may be straight (i.e., linear) or curved/bent (i.e., non-linear)
along its length (l). The mandrel 24 may be formed from a solid
material such as a metallic material, or it may be formed from a
solid soluble material such that it may be removed from the
composite truss structure 10 by treatment with a suitable solvent
as described in further detail below. In any event, the
mandrel-loading step depicted in FIG. 4 may be repeated as needed
to provide a required number of fabric-loaded mandrels 28 for the
fabric molding procedure discussed below.
FIGS. 5-14 depict a series of steps and intermediate structures
that may be involved in preparing a dry fabric mold 36 (see FIG.
11) which may provide the fabric skeleton of the composite truss
structure 10. As shown in FIG. 5, one or more first dry fabric
layers 38 may first be placed on a tool 40 that may have a
non-corrugated surface which may be smooth and flat, gradually
curved, or even abruptly bent at certain locations depending on the
structure of the desired component. The first dry fabric layer 38
may consist of one or more layers of woven or nonwoven fiber fabric
that is dry or not pre-impregnated with a resin, and it may provide
the fabric skeleton of the first facesheet 12.
In order to form the fabric skeleton of the truss elements 18, a
first layer of fabric-loaded mandrels 28 may be placed on the first
dry fabric layer 38, as shown in FIG. 6. More specifically, the
bases 30 of each of the fabric-loaded mandrels 28 may be placed in
contact with the first dry fabric layer 38 such that the first
layer of fabric-loaded mandrels 28 creates a corrugated surface 44
with grooves 46, as best shown in FIG. 7. As a non-limiting
possibility, the fabric-loaded mandrels 28 may be aligned in
abutment and in parallel such that the grooves 46 may extend
parallel to each other, as shown. However, other configurations are
certainly possible, particularly when using curved or bent
mandrels.
Turning now to FIG. 8, a next step involved in forming the fabric
skeleton of the truss elements 18 may involve placing a second
layer of fabric-loaded mandrels 28 on the first layer of fabric
loaded mandrels 28 by positioning each of the fabric-loaded
mandrels 28 of the second layer in a respective one of the grooves
46. More specifically, the top 32 of each fabric-loaded mandrel 28
of the second layer may be placed in contact with or at least
oriented toward a bottom 48 of each groove 46, such that the base
30 of each fabric-loaded mandrel 28 of the second layer may be
oriented upward to provide a flat or substantially flat surface. In
this way, the second layer of fabric-loaded mandrels 28 may be
interdigitated with the first layer of fabric-loaded mandrels 28.
Optionally, additional layers of the fabric-loaded mandrels 28 may
be stacked on the first and second layers of the fabric-loaded
mandrels 28 according to the steps depicted in FIGS. 6 and 8 to
provide a core with additional truss elements (see FIG. 9).
After building-up the desired number of layers of the fabric-loaded
mandrels 28, one or more second dry fabric layers 50 may be placed
over the fabric-loaded mandrels 28 to provide the dry fabric mold
36, as shown in FIGS. 10-11. If more than two layers of
fabric-loaded mandrels 28 are used, one or more second dry fabric
layers 50 may be placed over all of the layers of fabric-loaded
mandrels 28, as shown by example in FIG. 12, or one or more second
dry fabric layers 50 may be placed at desired positions between the
layers of fabric-loaded mandrels 28, as shown by example in FIG.
13. The second dry fabric layer 50 may provide the fabric skeleton
of the second facesheet 14 and it may consist of one or more layers
of woven or nonwoven fiber fabric that is dry or not
pre-impregnated with resin. However, in some arrangements, the
second dry fabric layer 50 may be eliminated from the dry fabric
mold 36 when only a single facesheet in the composite truss
structure is desired.
If any gaps 52 are present in the dry fabric mold 36, such as
between the fabric-loaded mandrels 28 and either or both of the dry
fabric layers 38 and 50, a filler material 54 may optionally be
inserted in each of the gaps 52 to provide a more compact mold (see
FIG. 14). The filler material 54 may be formed from dry fiber
fabric and it may have any shape suitable to fill the gaps 52. As a
non-limiting example, the filler material(s) 54 may have a tubular
shape configured to fill any gap(s) 52 extending along the length
(l) of the fiber-loaded mandrels 28 and located between the
fiber-loaded mandrels 28 and either or both of the dry fabric
layers 38 and 50.
Referring now to FIG. 15, once the dry fabric mold 36 is prepared
and any optional filler material(s) 54 are installed, the dry
fabric mold 36 may first be infused with resin by a resin infusion
process 55, and then subjected to a curing process 56. The resin
infusion process 55 may be carried out by placing the dry fabric
mold 36 and the tool 40 in a vacuum bag 58, evacuating the vacuum
bag 58, and drawing resin into the vacuum bag 58 with vacuum
pressure to cause the dry fabric mold 36 to become infused with the
resin. The curing process 56 may then be carried out by heating the
vacuum bag 58 carrying the resin-infused dry fabric mold 36 in an
oven at a suitable temperature and pressure to cause the resin to
cure to a hardened state. However, the curing process 56 may be
carried out in the absence of heat as well. During the curing
process, the resin-infused fabric may be fused together as a single
unit to provide the composite truss structure 10 having the first
facesheet 12, the second facesheet 14, and the truss elements 18
integrated as one-piece.
After removing the cured composite truss structure 10 from the
vacuum bag 58, the mandrels 24 may be removed from the composite
truss structure 10 using a tool, or they may be pulled or pushed
out manually from the composite truss structure 10, as depicted in
FIG. 16. Alternatively, if the mandrels 24 are soluble mandrels,
they may be dissolved by treating the mandrels 24 with a solvent 60
that is capable of dissolving the mandrels 24 without significantly
disturbing the integrity of the composite truss structure 10 (see
FIG. 17). As one possibility, the solvent 60 may be water if the
mandrels 24 are water soluble, although other suitable solvents may
also be used. Notably, the use of soluble mandrels may improve the
ease of removing mandrels 24 from composite truss structures having
angled facesheets (see FIG. 3, for example) and/or otherwise closed
arrangements in which access to the mandrels 24 may be hindered by
the facesheets.
The resulting composite truss structure 10 may be formed as a
larger panel 62 that may be sliced or cut as needed to provide a
desired number of individual components 64, as schematically
depicted in FIG. 18. In this regard, the dimensions of the panel 62
may scaled as needed according to the dimensions of the
component(s) 64 as well as the desired number of components. As
will be appreciated, the rate of production of the components 64
may be markedly improved by cutting the components 64 from the
larger panel 62, as opposed to molding the components 64
individually.
FIG. 19 summarizes the steps that may be involved in manufacturing
components with the composite truss structure 10. Beginning with a
first block 70, one or more mandrels 24 may be loaded with a dry
fabric tube 26 to provide a desired number of fabric-loaded
mandrels 28, as shown in FIG. 4 and described above. With the
fabric-loaded mandrels 28 at hand, the dry fabric mold 36 may be
prepared according to a block 72. The block 72 may involve: 1)
placing the first dry fabric layer 38 on the tool 40 (block 74/FIG.
5), 2) placing a first layer of fabric-loaded mandrels 28 on the
first dry fabric layer 38 to form the corrugated surface 44 (block
76/FIGS. 6 and 7), 3) placing a second layer of fabric-loaded
mandrels 28 on the first layer of the fabric-loaded mandrels 28
(block 78/FIG. 8), and 4) placing a second dry fabric layer 50 over
the fabric-loaded mandrels 28 (block 80/FIG. 10). However,
additional layers of fabric-loaded mandrels 28 (i.e., more than
two) may be stacked on the first two layers by repeating the blocks
76/78 as desired prior to the block 80 (see FIG. 9). If more than
two layers of fabric-loaded mandrels 28 are used, a second dry
fabric layer 50 may be placed over multiple layers of fabric-loaded
mandrels 28 (see FIG. 12), or one or more second dry fabric layers
50 may be placed at desired positions between layers of
fabric-loaded mandrels (see FIG. 13). In addition, a single layer
of the fabric-loaded mandrels 28 may be used to mold the truss
elements 18, in which case the block 78 may be eliminated. It is
also noted that the block 80 may be eliminated in cases where only
a single facesheet is desired in the final product. Optionally, the
block 72 may further involve inserting one or more of the filler
material(s) 54 in any gaps 52 remaining in the dry fabric mold 36
(block 82/FIG. 14).
According to a next block 84, the dry fabric mold 36 may be infused
with resin by the resin infusion process 55 as described in detail
above. The resin-infused molded fabric may then be cured to provide
the composite truss structure 10 formed as a larger panel 62
according to a next block 86 (also see FIG. 15). The mandrels 24
may then be removed from the composite truss structure 10 by
tool-assisted removal, manual removal, or by treatment with a
solvent if the mandrels 24 are soluble (block 88/FIGS. 16-17).
Lastly, the composite truss structure 10 may be sliced or cut into
individual components 64 having desired dimensions (block 90/FIG.
18). In some cases, the component(s) 64 cut from the panel 62 may
form portions of a larger, complete component, such that the
components 64 may be further assembled with additional components
to provide the complete component.
INDUSTRIAL APPLICABILITY
In general, it can therefore be seen that the technology disclosed
herein has industrial applicability in a variety of settings
including, but not limited to, manufacturing of composite truss
structures for aerospace applications or other industrial
applications. The composite truss structures disclosed herein may
have strengths comparable with honeycomb-stiffened composite
sandwich structures of the prior art, but they may be manufactured
in significantly fewer steps. In particular, the use of mandrels to
mold dry fiber fabrics into the shape of a complex truss structure
permits the application of a single resin infusion step and a
single curing step to provide a fused, one-piece composite
structure. In this way, the multiple curing stages and hot
debulking steps that are characteristic of prepreg manufacturing
methods of the prior art are avoided and the ease and efficiency of
accessing complex composite truss structures for various industrial
applications may be markedly improved. Moreover, while the
nonflexible composite truss structure disclosed herein could
conceivably be fabricated using carbon fabric prepregs instead of
dry fabric material, prepreg material is typically only available
as flat sheets (not tubes), such that the covering of truss
element-shaped mandrels may require a wrapping type process in
which the mandrels are rolled-up in the carbon prepreg layers and
overlapped at the edges. As a result, this alternative method may
be susceptible to wrinkling and may require additional hot
debulking steps to smooth out the joints and/or wrinkles in the
carbon prepreg layers. In contrast, the method disclosed herein
employs dry fabric braided tubes that may be compressed and
stretched over the mandrel to provide a tight fit that requires no
hot debulking. In addition, the molding of the composite truss with
dry fiber fabric may be a more cost-effective approach, as carbon
prepregs are generally more expensive than dry fiber fabric. It is
expected that the technology disclosed herein may find wide
industrial applicability in a wide range of areas such as, but not
limited to, aerospace applications.
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